1. Field of the Invention
The present invention relates to an ultrasonic imaging apparatus as well as an ultrasonic low attenuation medium, and in particular, to a technology for obtaining the scanned position when an image is obtained by scanning a subject to be examined using ultrasonic waves.
2. Description of the Related Art
The ultrasonic imaging apparatus is capable of obtaining images expressing heartbeats or movements of a fetus in real time by a simple operation of applying an ultrasonic probe on the body surface of a subject to be examined. Further, because of the high degree of safety, the examination may be repeated. Furthermore, compared to other diagnostic apparatuses such as an X-ray diagnostic apparatus, X-ray CT apparatus, MRI apparatus, or the like, the size of the system is small, and therefore, it is convenient to conduct examinations at bedsides. Moreover, ultrasonic diagnosis may be used in obstetrics, home care, and the like, without being influenced by the dosage, unlike X-rays.
Further, the ultrasonic imaging apparatus is also frequently used in the examination of breast cancer as with X-ray mammography. X-ray mammography is excellent in its ability to detect microcalcification; however, the ultrasonic waves are said to be more superior in depicting the soft tissues of a living body. Furthermore, X-ray mammography may cause pain, depending on the subject to be examined, since the breasts are sandwiched by pressurizing plates for imaging; however, ultrasonic diagnosis does not cause pain, and, in this respect, ultrasonic diagnosis is said to be more superior to X-ray mammography.
Additionally, in diagnoses using the ultrasonic imaging apparatus, an acoustic coupler to be disposed between the ultrasonic probe and the body surface of the subject to be examined is used in some cases.
The following may be cited as a reason for using an acoustic coupler. For example, in diagnosing a part such as the thyroid gland or carotid artery, an acoustic coupler is used to give some distance between a diagnostic part existing on the body surface and the surface of the ultrasonic probe. Since it is difficult to converge ultrasonic beams directly below the ultrasonic probe, there is a problem of deteriorating the resolution in the region directly below the ultrasonic probe. Therefore, the body surface of the subject to be examined and the surface of the ultrasonic probe are separated so as to enable convergence of ultrasonic beams on the body surface by arranging an acoustic coupler between the ultrasonic probe and the body surface of the subject to be examined.
Also, an acoustic coupler may be used in an automatic diagnostic system (for example, Published Japanese Translation of a PCT No. 2002-512835, Japanese Examined Patent Publication (Kokoku) No. H04-4896). For instance, when applying an ultrasonic probe to a diagnostic part having a curved surface such as the breasts to automatically scan it, linearly scanning via an acoustic coupler, rather than scanning the diagnostic part by directly applying the ultrasonic probe following the curved surface, provides simplified automatic control and a driving mechanism.
The automatic scanning of an ultrasonic probe is described with reference to FIG. 1. FIG. 1 provides a side-view for describing the automatic scanning of an ultrasonic probe. For example, in using water as an acoustic coupler, the breast P is submerged in a water tank 103 filled with water to transmit/receive ultrasonic waves via the acoustic coupler (water). In this case, a movable stage 102 is connected to an ultrasonic probe 100 and is moved via a motor 101 to linearly move the ultrasonic probe 100. As described, automatic scanning may be easily realized by linearly moving the ultrasonic probe 100 through the water tank 103 filled with water (acoustic coupler).
Further, various contraptions have been made for the material or the manufacturing method of an acoustic coupler in order to prevent deterioration of the image quality attributed to excessive attenuation or multiple reflections of the ultrasonic waves accompanied by the acoustic coupler (for example, U.S. Pat. No. 3,288,138, U.S. Pat. No. 3,272,792, Japanese Unexamined Patent Application Publication (Kokai) No. H03-32652).
Furthermore, the ultrasonic imaging apparatus is provided with a body mark function. A body mark is composed of a simplified figure of the diagnostic part and an ultrasonic probe. Marking the position where a tomographic image has been obtained and recording the same along with the tomographic image makes it easier to capture the diagnostic part at the time of diagnostic reading.
One example of a body mark is shown in FIG. 2A and FIG. 2B. In FIG. 2A, the body mark for a liver is shown, and in FIG. 2B the body mark for a breast is shown. The operator may manually move the probe mark Pr representing the position and the orientation of the ultrasonic probe to a position of choice, and record the ultrasonic image at the obtained position by attaching the probe mark Pr.
In actuality, to image a liver or heart, body marks may not be used. When imaging a liver or heart, since characteristic structures such as the portal vein or gallbladder are depicted in the tomographic image, in many cases the position where the tomographic image has been obtained (scanned position) may be captured even without using body marks. Contrary to this, in the event of imaging breasts, body marks are used. Since the breast is symmetrically shaped having the papilla in the center, just by looking at the tomographic image, it is difficult to capture the position where the tomographic image has been obtained (scanned position). In the US and Europe, standard regulations for body marks, etc. have been proposed at academic conferences and similar forums.
However, the ultrasonic imaging apparatus is not necessarily widely used as a diagnostic apparatus for examining breast cancer. The reason is that the examination using ultrasonic waves relies largely on the skill or experience of the examining technologist. In a general ultrasonic diagnosis, the operator (examining technologist) obtains the tomographic image of the diagnostic part by an ultrasonic probe, and later the diagnostic reading of the tomographic image is conducted by a doctor. It is therefore essential to obtain a tomographic image with sufficient accuracy such that it is capable of undergoing diagnostic reading by the doctor. As for the tomographic image obtained by ultrasonic waves, since the image quality changes depending on the set up, such as the way the ultrasonic probe is applied or the gain setting of the apparatus, etc., the technologist is required to learn the scanning technology to be able to obtain an image quality that is satisfactory to the doctor conducting the diagnostic reading.
Moreover, even if the image quality is good, just a diagnostic reading of the tomographic image is insufficient to determine which region of the breast has been scanned to obtain the image. Further, it is also difficult to determine whether the entire region has been scanned or not. For recording, the body mark may be appended to the tomographic image. However, conventionally, since it is an operator (examining technologist) who determines the position where the tomographic image is obtained (scanned position) and inputs the position on the body mark manually, there is concern of a possible increase in examining hours or input errors. In an actual examination, since imaging of many patients within a short period of time is required, in some cases, the work of inputting the position where the tomographic image has been obtained is omitted, or a wrong position is entered. As described, if the input is omitted or if a wrong position is entered, then it becomes a problem to find out which region has been scanned to obtain the tomographic image.